The present invention relates to new radiation synovectomy compositions and to the use of such compositions. Certain of the compositions and their methods of preparation are also new.
Over two million people in the United States suffer from rheumatoid arthritis. The major cause of pain and physical disability for these individuals comes from destruction of the diarthroidal or synovial joints. The disease will involve the hands (metacarpophalangeal joints), elbows, wrists, ankles and shoulders for most of these patients, and over half will have affected knee joints. Untreated, the joint linings become increasingly inflamed resulting in pain, loss of motion and destruction of articular cartilage. One medical therapy applied to this disease involves the use of chemicals to attack and destroy the inflamed synovium (chemical synovectomy); however, the agents employed are highly systemically and locally toxic and capable of damaging articular cartilage. Similar toxicity concerns arise when repeated injections of corticoid steroids are used. In several cases where chemical therapy has failed, surgery is employed to remove the inflamed joint lining (surgical synovectomy). However, the difficulty of removing all the diseased synovium often leads to regrowth with recurrence of symptoms. If surgery is successful, freedom from symptoms usually lasts two to five years. When the symptoms reappear, surgical reintervention is not an option due to the presence of fibrosis and scar tissue which result from the previous surgery.
Radiation synovectomy has been used in Europe for many years to substantially ablate or destroy the inflamed synovium. The procedure is simple, involving only the injection of a radionuclide of the appropriate characteristics into the synovial cavity. The primary disadvantage of this technique has been the unacceptable radiation doses to non-target organ systems due to leakage of radioactive material from the cavity and difficulty in delivering a .beta.-particle of the appropriate energy for the size joint being treated. The chemical nature of current radiation synovectomy agents is such that leaked materials tend to be retained by liver, spleen and lymph nodes. The leakage problem is often due either to the difficulty of formulating the correct particle size or to lack of a tight binding of the nuclide to the particle. Another disadvantage is the use of radionuclides that don't have the appropriate beta energy to treat the inflamed synovium.
A radiation synovectomy agent that, would not have the foregoing disadvantages would have the following characteristics:
1. The radionuclide used in the agent should have a beta energy sufficient to penetrate and ablate the enlarged synovial tissues, but not so great as to damage underlying articular cartilage or overlying skin. Any accompanying radiation should not generate an unacceptable extraneous radiation dose to the patent. The nuclide used may vary depending on the size of the joint and the beta energy necessary to ablate the synovial tissues in that joint.
2. The radionuclide should be attached to a particle of sufficient size so that it will not leak to any great extent from the diseased joint but still be able to be phagocytized in the synovium of the joint.
3. The binding between the radionuclide and the particle should be essentially irreversible through the course of radiotherapy (usually this duration of therapy is determined by the half life of the particular isotope).
4. The particle should preferably be biodegradable, i.e., it should be removable from the joint by the normal biological degradation mechanisms in the joint, itself, and should be cleared from the body in standard ways in a rapid manner with little or no toxicological effects.
5. If radioactive material should leak from the synovial cavity, the radionuclide should be released in a chemical form that rapidly egresses from the body, as for example, an anion which is excreted efficiently through the renal system. Preferably, the radionuclide would stay attached to a chelate or some portion of the degraded particle if this would facilitate clearance from the body.
An object of the present invention is to provide radiation synovectomy compositions containing a radiation synovectomy agent meeting substantially all of the foregoing criteria.
This invention relates to a radiation synovectomy composition for treating, e.g., by ablation, the inflamed synovium of a synovial joint of a person suffering from rheumatoid arthritis. It comprises a radionuclide or radionuclide complex bound to a substantially insoluble particle as the radiation synovectomy agent in a sufficient amount to provide satisfactory synovectomy when administered with a pharmaceutically acceptable radiation synovectomy vehicle. The radionuclide is a beta emitter that would substantially ablate or destroy the diseased synovium, but will not significantly damage underlying articular cartilages or overlying skin. The radionuclide complex is substantially kinetically stable, but should degradation lead to leakage from the joint after administration, the radioactive material will rapidly clear from the body. A substantially kinetically stable complex as known to those skilled in the art is a complex which under normal biological conditions is kinetically stable, but not necessarily 100 percent kinetically stable in each and every patient application since biological systems vary somewhat. However, the necessary stability of the complex is determinant upon the half-life of the radioisotope being used. After the isotope has decayed to the point of being insignificant, the stability of the complex is no longer important. The particle size of the agent is of sufficient size such that there is essentially little or no leakage of the intact radionuclide complex-particle unit from the synovial joint after administration. Additionally, the size and properties of the particle can be defined and controlled before it is bound to the radionuclide complex resulting in an agent having good synovectomy properties. Also, the binding of the radionuclide complex can be controlled resulting in better reproductivity and more complete binding and better in vivo clearance.
A further feature of the present invention is the use of the radiation synovectomy compositions to treat inflamed synovia of people afflicted with rheumatoid arthritis. Another feature of the present invention is directed to novel radiation synovectomy agents. Another feature of the present invention is that by the nature of the labelling process, any in vivo decomposition that generates joint leakage produces radioactive materials in a form that clear rapidly from the body.
As mentioned, the radiation agent comprises a substantially insoluble particle which is of suitable size as to not substantially leak from the joint after administration. Normally, the size may be from approximately 0.5 to 40 microns. These particles are preferably biodegradable (but can also be degradable by other mechanisms) and not prone to aggregation under the conditions used to prepare or store the radiation synovectomy agent. The particle should have a density of approximately 0.7 to 2.0 gm/ml, preferably from 0.7 to 3.5 gm/ml, and should be suspendable in pharmaceutically acceptable vehicles. Some of the material from which such particles can be made include latex, derivatized polystyrene, silica, alumina, albumin (such as albumin microspheres), other proteins, polycarbonates, cellulose and inorganics, e.g., sulfur (colloid) glass (beads), hydroxyapatites, calcium phosphates or calcium pyrophosphates. For purposes of this application, the term "hydroxyapatite(s)" shall include materials known as hydroxyapatite(s) and also as hydroxylapatite(s). These two terms have been used previously in the literature to refer to the same materials. Examples of hydroxyapatites for this application include matrix prepared from the bones and or teeth of animals and matrix prepared by inorganic synthesis, each being more amorphous than crystalline in composition. This includes calcium-hydroxy-hexaphosphate (3(Ca.sub.3 (PO.sub.4)2)Ca(OH).sub.2 ; also given as 2[Ca.sub.5 (PO.sub.4).sub.3 OH]). The particles have sites on the surface that permit absorption or covalent binding of the radionuclide or radionuclide complex. Such sites can include but are not limited to--NH.sub.2, --SH, --OH, &gt;C.dbd.O, calcium, hydroxyl, phosphate and similar such sites, and hydrophobic or hydrophilic regions or pockets. In addition to being insoluble, the particles must be non-toxic and preferably non-allergenic. Preferred particles include albumin microspheres, sulfur colloid, hydroxyapatite and hydroxyapatite-like matrix.
When using hydroxyapatite or hydroxyapatite-like matrix, the particle size thereof becomes important. This is because of reports that hydroxyapatite particles may become phagocytosed and solubilized by synovial fibroblasts. In particular, it is believed that the hydroxyapatite particles are first solubilized by phagocytosis and then dissolved in the acidic environment of secondary lyposomes.
Therefore, it is necessary to establish means to maintain the hydroxyapatite of the radiation synovectomy agent for an effective period of time in the synovial cavity. In particular, the rate of solubilization of the hydroxyapatite should optimally be much slower than the half-life of the radioisotope used in the radiation synovectomy agent. In this manner, the radioisotope may completely decay before dissolution of the hydroxyapatite particle. It has been determined that the rate of solubilization and dissolution of hydroxyapatite is a function of particle size, wherein smaller particles are more quickly phagocytosed and dissolved than larger particles. A complete study of rate of solubilization and dissolution as a function of particle size for hydroxyapatite particles has not yet been carried out. However, studies have suprisingly shown that there is no significant lower limit on particle size. In particular, there have been no problems associated with leakage regardless of particle size. For practicle purposes, a particle size of 0.5 microns or greater is preferred, however, smaller particle sizes would be acceptable. It is believed that this is because of the relatively high charge of hydroxyapatite and the tendency of hydroxyapatite particles to aggregate.
Maximum particle size is approximately 40 microns. If particles are too large, e.g. greater than 40 microns, the particles can not be surrounded by cells and will not be easily phagocytosed and dissolved. This can disadvantagously cause dead fibrous areas too occur in the synovium.
In light of the above, when using hydroxyapatite particles as the particles of the radiation synovectomy agent according to the present invention, it is desirable that the hydroxyapatite particles have a particle size of 0.5 to 40 microns.
The radioisotopes that can be used are those that emit beta particles and are such that after administration will ablate the diseased synovium but will not significantly damage the underlying articular cartilage or overlying skin. These isotopes should have an average beta energy between 0.25-2.75 Mev, with or without an imageable gamma ray, with mean soft tissue penetration of about 0.70 and 25.0 mm, and with a half-life of between 0.05 and 700 hours. Examples of preferred beta emitting isotopes include 198-Au, 188-Re, 186-Re, 177-Lu, 176m-Lu, 175-Yb, 169-Er, 166-Ho, 165-Dy, 156-Sm, 153-Sm, 115m-In, 105-Rh, 90-Y, 51-Cr, 77-As, 67-Cu and 32-P, in addition to others of the lanthanide group such as, 141-Ce, 144-Pr, 147-Nd, 148-Pm, 152-Eu, 153-Gd, 157-Tb and 170-Tm. Preferably the isotope would either have an imageable gamma ray or could be doped with an isotope that would contain an imageable gamma ray. This doping isotope could be of the same or different element providing that its chemistry is sufficiently similar to the beta emitting isotope so that its biodistribution in the present use would be close or identical to the beta emitter. Preferred isotopes include: 186-Re, 188-Re, 90-Y, 153-Sm, 77-As, 105-Rh, 177-Lu, 176m-Lu and 166-Ho.
The radionuclide complexes that can be used are those that are stable before and after administration to the synovium joint. Additionally, if such complex leaks from the joint it will be rapidly cleared from the body. This will be the case even if the complex becomes separated from the insoluble particle. The complexes are formed by complexing the radionuclide under complexing conditions with a suitable ligand to provide a complex with the foregoing properties. Ligands that can be used are preferably polydentate, i.e., containing more than two coordinating atoms per ligand molecule. A coordinating atom is defined as one that has a free pair of electrons which can be bonded to the radionuclide. This atom is preferably separated by two or more atoms from any other coordinating atom. The coordinating atoms are chosen from nitrogen, oxygen, sulfur, phosphorus or carbon with nitrogen and/or oxygen and/or sulfur being the preferred coordinating atoms. Examples of chelates include all phosphonate carboxylate and amine carboxylate ligands, MAG.sub.3 (mercaptoacetylglycylglycylglycine), all polycarboxylic acid-amine ligands especially DTPA (diethylenetriaminepentaacetic acid), e.g., EDTA (ethylenediaminetetraacetic acid), DADS (N,N'-bis(mercaptoacetamido)ethylenediamine and CO.sub.2 -DADS N,N'-bis(mercaptoacetamido)-2,3-diaminopropanoic acid) and their derivatives (see European Application 0173424 and U.S. Pat. No. 4,673,562), mono- and poly-phosphonates, BATs (N,N'-bis(2-mercaptoethyl)ethylene-diamine) and derivatives (see European Applications 0163119 and 0200211), thiosemicarbazones, PnAO and other amine-oxime ligands (See European Applications 0123504 and 0194843), marcocyclic and open chain tetra-, penta-, hexa-, hepta- and octacoordinating nitrogen-containing compounds with or without other coordinating atoms or unsaturation. Examples of preferred phosphonate ligands include but are not limited to those specified in U.S. Pat. Nos. 4,234,562; 3,983,227; 4,497,744; 4,233,284; 4,232,000; 4,229,427; and 4,504,463; preferably HEDP (hydroxyethyldiphosphonate), PYP (pyrophosphate), EDTMP (ethylenediaminetetramethylphosphate), and HMDP (hydroxymethylenediphosphonate).
Other ligands include MAG.sub.3, DTPA, BAT, DADS and PnAO type ligands which have been modified so that they are bifunctional, i.e., can coordinate the radionuclide and also be coupled to the particle. Preferred complexes include: MAG.sub.3, DADS, hydroxyapatite or hydroxyapatite-like matrix complexed with 186-Re, 188-Re, 105-Rh, 153-Sm or 156-Sm.
The radiation agent of this invention can be prepared by attaching or binding to the particle the desired isotope under standard conditions for attachment. This involves coupling a ligand (either with or without a radioactive atom) to the particle with or without the presence of a spacer between the two units. Generally, the coupling can be done by any group(s) attached to the ligand that is (are) not crucial for complexing the radioisotope in a stable manner. This coupling portion of the ligand may consist of any group that can easily and specifically bind covalently to functional groups on the particle or that may simply adsorb very strongly to the surface of the particle. Examples of the covalent coupling would include aminocarboxylate, carboxylate or phosphonate ligands which would combine with Ca.sup.2+ at or near the surface of the particle, activated esters of carboxylic acids which would combine covalently to amine groups, to sylates and acid halides which would combine with OH groups and maleimides which would combine with thiol groups, with the thiol, amine and OH groups assumed to be at or near the surface of the particle.
The following methods of preparing the desired radiation synovectomy agent may be used:
(a) The pre-formed method: One of the previously described radionuclide complexes is covalently bonded to one of the previously described particles having functional groups. Step one--a particle of the optimal size, (e.g., 1-10 microns, 5-50 microns) and composition (e.g., hydroxyapatite, hydroxyapatite-like matrix, albumin, polycarbonate, cellulose, glass, latex) and having appropriate residues (amines, hydroxyls, hydroxide, phosphate, carboxylates, thiols) is selected. Step two--a radioisotope (of the appropriate nuclear characteristics) which has been incorporated into a ligand (i.e., a radionuclide complex) is covalently bonded to the particle.
(b) The post-formed method: A ligand is covalently bonded to one of the previously described particles. Thereafter, one of the previously described radioisotopes is incorporated into the covalently bonded complexing ligand, after the radionuclide has been treated in such a way, e.g., using a transfer ligand such as citrate or tartarate to facilitate transfer of the radionuclide to the ligand, to make it bind more readily to the ligand.